The pharmaceutical industry employs a variety of dosage formulations for orally administering medicinal agents to patients. Typical formulations for oral administration include liquid solutions, emulsions, or suspensions, as well as solid forms such as capsules or tablets. Solid oral dosage formulations are usually intended for adults who car easily swallow large tablets whole, the often disagreeable taste of the active ingredient need not be taken into account in formulating the medicine, except for the provision of means to prevent the taste from being apparent during the short time that the medicine is in the mouth. Such means may include the provision of an appropriate coating on the tablet, the use of a capsule form (the gelatin outer shell of the capsule keeps the active ingredient inside until the capsule has been swallowed), or simply firmly compressing a tablet so that it will not begin to disintegrate during the short time that it is intended to be in the mouth.
Children, older persons, and many other persons have difficulty swallowing whole tablets and even capsules. Therefore, it is often desirable to provide the medicine either in liquid form or in a chewable solid form or an alternative solid form, e.g., small particles which can be sprinkled onto soft food and swallowed intact with the food, in addition to the tablet or capsule intended to be swallowed whole. A oral liquid dosage form has many advantages for pediatric patients and for elderly patients. Many medicines have bitter or an otherwise disagreeable taste and this can be a significant problem. A further requirement of any dosage form is that it must be bioavailable; that is, once the formulation reaches the stomach, the formulation should release the active ingredient rapidly and completely to ensure that substantially the entire amount of the active ingredient is absorbed.
For some medicines the limited solubility of the drug in water can be a problem in formulation liquid oral dosage forms and in this case a suspension is often used. However, a suspension can present it's own type of problem if the drug has some solubility in water the tiny particles held in an aqueous suspension can change in crystal form or size. This can present problems in maintaining proper bioavailability either because crystal size can affect absorption rate or because the re-crystallization process can alter the polymorphic form of the suspended crystals and the altered form may have a different bioavailability. Thus there is a need for a suspension formulation that reduces the rate of re-crystallization and/or change in polymorphic form of a slightly soluble crystalline compound such as carisbamate.